Tooth mineral of enamel and dentine is principally a CO3-containing hydroxyapatite. The initial research proposal and this continuing study is based on the premise that the crystallographic properties (i.e., crystallite size, unit-cell dimensions, morphology, internal strain), spectroscopic properties (bonding effects), and composition of the tooth mineral have jointly fundamental, although not exclusive roles in the caries susceptibility of tooth. The immediate objectives are: (1) to determine the crystallographic, spectroscopic properties and composition of dental apatites as function of: (a) species (using human, and other species reported to demonstrate higher or lower caries susceptibility than human); (b) age of human tooth (using pre-eruptive, deciduous and mature teeth from different age groups); (c) trace element contents (using human teeth obtained from regions in the USA of high and low caries incidence; (2) to determine the mechanism behind the cariostatic effect of Fluoride as it relates to the tooth mineral (using the naturally fluoridated shark's tooth and non-fluoridated human tooth); (3) to determine the effects of reportedly cariostatic and cariogenic trace elements (individually and in combination with F or CO3 on the crystallographic and spectroscopic properties and thermal stability of synthetic apatites in order to better assess their role in dental caries); (4) to define the role of 'H2O', CO3, Mq, HPO4 in enamel apatite and their possible role in caries. The long-term goal is to define the structural and compositional factors relating to the caries susceptibility of enamel apatites, X-ray diffraction, IR spectroscopy, TGA-DTA, EM and SEM will be used in the investigation of synthetic and dental apatites.